1. Field of the Invention
The present invention relates to a linear motor comprising permanent magnets embedded in a field magnet yoke.
2. Description of the Related Art
A variety of linear motors or pulse motors, which are provided with permanent magnets, have been suggested. Taking notice of the method for providing the permanent magnets, the following linear motors or pulse motors are representatives.
A variable reluctance type linear pulse motor comprises a permanent magnet joined to an iron core, the permanent magnet being disposed near an upper portion of the iron core provided with an exciting coil, and a magnetic pole plate for interposing the permanent magnet together with the iron core (see Japanese Laid-Open Patent Publication No. 63-294252). Another variable reluctance type linear pulse motor comprises permanent magnets which are arranged in a divided manner (see Japanese Laid-Open Patent Publication Nos. 2-307356 and 2-32750).
However, in the linear pulse motor disclosed in any one of Japanese Laid-Open Patent Publication Nos. 63-294252, 2-307356, and 2-32750, the iron core cannot be miniaturized because the permanent magnet is provided on the upper excitation side.
A linear pulse motor comprises first and second rotors or reaction plates which are arranged on both upper and lower surfaces of a stator and which are mechanically fixed respectively, each of the first and second rotors being formed with a U-shaped core, the core being divided into two to arrange a permanent magnet therebetween so that the magnetic flux flows from one to the other, and the core being applied with an exciting wiring wound therearound (Japanese Laid-Open Patent Publication No. 64-47258).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 64-47258, the permanent magnet is provided on the field yoke, and it is impossible to miniaturize the field yoke.
A linear pulse motor comprises a permanent magnet which is provided for iron core teeth disposed on the excitation side of a rotor, and a slit which is provided for a non-magnetized portion. The linear pulse motor comprises a permanent magnet which is provided for iron core teeth of a stator, and a slit plate which has a slit at a non-magnetized portion (Japanese Laid-Open Patent Publication No. 1-298945).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 1-298945, the iron core including the slit plate cannot be miniaturized.
A linear pulse motor comprises, at a forward end of a magnetic pole for constructing an electromagnet of a rotor, a permanent magnet which generates a magnetomotive force in a direction perpendicular to a direction of a magnetomotive force generated by the electromagnet, or a permanent magnet which generates a magnetomotive force in a direction parallel to the direction of the magnetomotive force generated by the electromagnet (Japanese Laid-Open Patent Publication No. 2-114852).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 2-114852, the electromagnet cannot be miniaturized because the permanent magnet is provided at the forward end of the magnetic pole.
A linear pulse motor comprises magnetic pole blocks arranged with small teeth disposed on outer circumference in an axial direction, permanent magnets for magnetizing the magnetic pole blocks to give predetermined magnetic poles, and the magnetic pole blocks being magnetized to have mutually different magnetisms by the permanent magnets, in which tips of the teeth of one magnetic pole block are opposed to tips of teeth of a protruding magnetic pole of a stator, while tips of the other magnetic pole block are opposed to bottoms of teeth of the protruding magnetic pole of the stator (Japanese Laid-Open Patent Publication No. 6-197517).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 6-197517, the linear pulse motor cannot be miniaturized because of the presence of the magnetic pole block.
A linear pulse motor comprises a rotor having a rotor iron core formed with a plurality of small rotor teeth disposed at equal pitches in an axial direction while opposing to small stator teeth on an outer circumferential surface, in which a cylindrical member composed of a non-magnetic material is provided between a shaft of the rotor and the iron core of the rotor (Japanese Laid-Open Patent Publication Nos. 7-170719 and 8-9623).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication Nos. 7-170719 and 8-9623, the linear pulse motor cannot be miniaturized because the cylindrical member is disposed between the shaft of the rotor and the iron core of the rotor.
A linear pulse motor comprises a permanent magnet for magnetizing rotor iron cores spaced from each other by predetermined axial distances into N magnetic poles and S magnetic poles respectively, in which a rotor shaft is composed of a magnetic material or a non-magnetic material, the permanent magnet is cylindrical, and the permanent magnet is arranged between the rotor iron core and the rotor shaft (Japanese Laid-Open Patent Publication No. 7-288969).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 7-288969, the linear pulse motor cannot be miniaturized because of the presence of the permanent magnet.
A linear pulse motor comprises permanent magnets magnetized in an axial direction, the permanent magnets being interposed between rotor cores spaced from each other by predetermined axial distances (Japanese Laid-Open Patent Publication No. 8-163857).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 8-163857, the linear pulse motor cannot be miniaturized because of the presence of the permanent magnet.
A linear pulse motor comprises magnetic pole units as rotors which include teeth composed of permanent magnets and magnetic substances arranged alternately at predetermined pitches and which are provided and separated by a predetermined gap with respect to a plurality of exciting units arranged at spacing distances of xe2x85x9 pitch to function as stators, one of the exciting units including magnetic poles arranged to intervene the magnetic pole unit on both sides, a magnetic substance for connecting the magnetic poles, and an armature coil wound around the magnetic substance (Japanese Laid-Open Patent Publication No. 10-327571).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 10-327571, the linear pulse motor cannot be miniaturized because of the presence of the permanent magnet.
A linear pulse motor comprises a permanent magnet arranged in a rotor having a plurality of small rotor teeth, in which the small rotor teeth are arranged at spacing distances of xc2xd of pitches of small stator teeth to constitute pairs of rotor cores with the permanent magnet magnetized in an axial direction between one small tooth and another small tooth, and the pairs are electrically insulated from each other by a gap or a non-magnetic substance (Japanese Laid-Open Patent Publication No. 11-41905).
However, in the linear pulse motor disclosed in Japanese Laid-Open Patent Publication No. 11-41905, the rotor cannot be miniaturized.
Further, the linear pulse motor using the permanent magnet as described above has no sufficient thrust force, in addition to the difficulty of miniaturization.
A general object of the present invention is to provide a linear motor which has a simple structure, which can be miniaturized, and which has a sufficient thrust force.
According to the present invention, there is provided a linear motor in which a thrust force is generated between a field yoke and electromagnets by an attraction and a repulsion based on polarities brought about for magnetic poles of permanent magnets embedded at predetermined pitches in the field yoke, magnetic poles formed on field yoke portions between the permanent magnets, and magnetic poles formed on the electromagnets by means of magnetization, and thus one of the field yoke and any unit including the electromagnets is relatively driven.
In the linear motor according to the present invention, the following relationships are established:
xcfx84e≈(2n+1)xcfx84p
xcfx84g=(2s+1/m)xcfx84e
wherein xcfx84p represents the spacing distance of the pitch of the permanent magnets embedded in the field yoke, xcfx84e represents the magnetic pole pitch of the electromagnets, xcfx84g represents the spacing distance of the pitch of the electromagnets, m represents the number of exciting phase or phases, n is 0, 1, 2, 3, . . . , and s is 1, 2, 3, . . . .
According to the linear motor of the present invention, the permanent magnets are embedded at the pitches xcfx84p≈xcfx84e/(2n+1) in the field yoke, and the electromagnets are formed at the positions of the pitches xcfx84g, i.e., xcfx84g=(2s+1/m)xcfx84e. In the linear motor, the field yoke or the electromagnets are driven in one direction at the step width xcfx84e/m.
According to the linear motor of the present invention, when the electric power is applied to a coil wound around a yoke portion for connecting respective legs, the respective legs can be magnetized to have opposite magnetic polarity.
The linear motor of the present invention also has the following feature. That is, a core of the electromagnet has two legs which are connected by a yoke for generating magnetic poles having opposite magnetic polarity, a wire is wound around the respective legs in opposite directions to form a differential coil thereby, and the respective legs are magnetized to have the opposite magnetic polarity by applying electric power to the differential coil.
According to the linear motor of the present invention, the respective legs can be magnetized to have the opposite magnetic polarity by applying the electric power to the differential coil.
According to the linear motor of the present invention, respective legs, which are disposed at both outer positions of the electromagnet, can be magnetized to have opposite magnetic polarity by applying electric power to a coil wound around a central leg of the three legs.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.